Field of the Invention
Embodiments of the present invention relate to a medical image processing technique and a radiotherapeutic technique that irradiate, with a beam, a focus being displaced by a patient's respiration and the like for practicing therapy.
Description of the Related Art
Radiotherapy is a therapeutic technique that irradiates a focus (cancer and the like) of a patient with a therapeutic beam and destroys the focus. Thus, unless irradiation with the therapeutic beam is correctly performed in registration with the position of the focus, there is a possibility that even normal tissue will be destroyed. To address this possibility, therapeutic planning is performed before a therapeutic operation of irradiating the patient with the therapeutic beam.
According to the therapeutic plan, the inside of the patient is CT-imaged, voxel data is obtained, and the position of the focus is three-dimensionally grasped, while the irradiation direction and irradiation intensity of the therapeutic beam are determined so as to achieve a small amount of irradiation onto normal tissue. Furthermore, in a case where the focus resides in a viscus (lungs or the like) being periodically displaced in synchronization with respiration and the like, the irradiation target and timing of the therapeutic beam toward the inside of the patient are examined.
In a stage of the therapeutic operation, the patient is fixed onto a bed at a radiotherapeutic apparatus, and the bed is moved so as to aim the beam from a beam irradiation port at the irradiation target examined in the therapeutic planning. The therapeutic beam is emitted from the beam irradiation port at a timing when the beam aim coincides with the focus being displaced in synchronization with respiration.
It is confirmed whether the beam aim coincides with the focus, by checking an X-ray fluoroscopic image taken though real-time imaging the patient on the bed using an X-ray imager permanently provided for the radiotherapeutic apparatus against a DRR (Digitally Reconstructed Radiograph) reconstructed from the voxel data used in the therapeutic planning into a two-dimensional image.
Unfortunately, X-rays output from the X-ray imager of the radiotherapeutic apparatus has a reduced intensity in order to attenuate the patient's exposure to radiation. Consequently, the focuses imaged in X-ray fluoroscopic images are often unclear. It is difficult to track the displacements of the focuses correctly.
Conventionally, methods are taken to address such cases. One of the methods implants a marker made of gold or the like in vicinity of the focus, and tracks the motion of the marker through the X-ray imager. Another method measures the motion of a body surface using a laser range finder. These methods then compensate the result of tracking the focus displacement.